We propose to test the hypothesis that interactions mediated by T cell receptors (TCRs) expressed on different T cell subsets play pivotal roles in immunoregulation and are directly involved in the control of autoimmune disease. In previous studies we showed that CD8+ T cells in vivo control the outgrowth of CD4+ cells mediating experimental allergic encephalomyelitis (EAE). Moreover, we showed that CD8+T cells also participate in the in vivo downregulation of CD4+Vbeta8+T cells following SEB administration. We investigated these CD4/CD8 interactions in vitro and observed that following SEB administration CD8+Tcells emerge which preferentially kill activated CD4+Vbeta8+ but not CD4+Vbeta8- T cells in vitro. This TCR Vbeta specific cytotoxicity was dependent on beta 2 microglobulin and was inhibited by antisera specific for Qa-1 but not by antibody to MEC class 1-a. This data suggest that the specificity of immune regulation involves recognition of TCR Vbeta determinants and Qa-1 molecules expressed on activated CD4+T cells. Recently, we extended these findings to show that CD8+ T cells isolated from CD4+Vbeta8+ T cell vaccinated mice specifically lyse a human B cell line cotransfected with both murine TCR Vbeta8 and Qa-1 cDNA, but not Bcells transfected with either TCR or Qa-1 cDNA alone. Furthermore, we showed that vaccinating naive mice with activated CD4+Vbeta8+ T cells specifically enhance SEB induced in vivo deletion of CD4+Vbeta8+ T cells. These in vivo and in vitro data support the idea that at least one consequence of T cell vaccination is the induction of CD8+ Vbeta specific CTL which downregulate immune responses. Because T cell vaccination has been used to ameliorate autoimmune disease in a variety of animal models and in humans, the overall goals of this project are to further define the cellular and molecular mechanisms involved in T cell vaccination. We will first confirm the observation that TCR Vbeta specific CD8+ regulatory T cells are induced by T cell vaccination. We will then extend our analysis to the EAE model to determine if Vbeta specific CD8+ T cells also mediate the protective effect of T cell vaccination against EAE. We will also determine if the molecular structure recognized by these regulatory CD8+ T cells is the TCR Vbeta chain or peptide(s) derived from the TCR Vbeta chain associated with Qa-1 molecules. Finally, we will directly determine if adoptive transfer of T cell vaccination induced TCR Vbeta specific CD8+ T cells regulate EAE in vivo.